In addition to blood draws, patients will undergo leukapheresis before beginning T-20 and possibly again when they restart HAART and at the end of the study. For this procedure, whole blood is collected through a needle placed in an arm vein, similar to donating blood. The blood circulates through a machine that separates it into its components. The white cells are then removed, and the red cells, platelets and plasma are returned to the body, either through the same needle used to draw the blood or through a second needle placed in the other arm. The white cells are used to study T cell function and levels and to detect hidden virus.